Copper foil composite including a release layer

ABSTRACT

A composite material includes a structural carrier layer and a relatively thin metal foil layer separated by a release layer. The release layer, that may be an admixture of a metal such as nickel or chromium and a non-metal such as chromium oxide, nickel oxide, chromium phosphate or nickel phosphate, provides a peel strength for the metal foil layer from the carrier strip that is typically on the order of 0.1 pound per inch to 2 pounds per inch. This provides sufficient adhesion to prevent premature separation of the metal foil layer from the carrier layer, but easy removal of the carrier layer when desired. Typically, the metal foil layer is subsequently bonded to a dielectric and the carrier layer then removed. The metal foil layer is then imaged into circuit features in the manufacture of printed circuit boards and flexible circuits.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a composite material having anintervening release layer. More particularly, a copper foil layer isreleasably bonded to a carrier layer for transport and assembly. Therelease layer disposed between the carrier layer and the copper foillayer facilitates separation. The copper foil layer may be laminated toa dielectric substrate in the manufacture of printed circuit boards.

[0003] 2. Description of Related Art

[0004] As electronic devices evolve, there is a need for thinner andsmaller printed circuits. This leads to a requirement for finer line toline spacing to increase circuit trace density.

[0005] Most printed circuit boards have a dielectric substrate, such asan epoxy or polyimide, laminated to a layer of copper foil. The copperfoil is etched into a desired circuit pattern. As the need for finerline resolution increases, thinner copper foil is required. This isbecause when copper foil is etched, etching occurs in both a verticaldirection and in a horizontal direction at about the same rate. Whilethe vertical etching is required to create spaces between adjacentcircuit traces for electrical isolation, horizontal etching at the baseof a trace damages the integrity of the circuit traces. Horizontaletching limits the minimum line-to-line spacing to approximately thethickness of the copper foil. Another problem with thicker copper foilis that a longer time is required to etch the foil increasing themanufacturing cost and increasing the environmental concern due to thedisposal or reclamation of dissolved copper.

[0006] One copper foil presently utilized in the manufacture of printedcircuit boards is referred to as one-half ounce foil. One square foot ofthis foil weighs approximately 0.5 ounce and has a nominal thickness ofabout 18 microns. Thinner copper foil, such as 9 micron thick foil, isavailable in the marketplace, however special care is required inhandling 9 micron foil to prevent wrinkling and damage.

[0007] Facilitating the handling of 9 micron, and thinner, foils is theuse of a carrier strip. The carrier strip is releasably bonded to thefoil for manufacturing and lamination. Once the foil is laminated andsupported by a dielectric, the carrier strip is removed. One commoncarrier strip is aluminum that may be removed by chemical etching, suchas by immersion in sodium hydroxide, without damage to the copper foil.Etching is time-consuming and disposal may create environmentalproblems.

[0008] Alternatively, a carrier layer, typically formed from copper, iscoated with a release layer. The copper foil layer is formed on therelease layer, typically by electrolytic deposition. Adhesion betweenthe release layer and the copper foil layer is high enough so that thecopper foil layer does not separate from the carrier layer prematurely,but is also sufficiently low that separation of the carrier layerfollowing lamination does not tear or otherwise damage the copper foillayer.

[0009] U.S. Pat. No. 3,998,601 to Yates et al. discloses a release layerformed from either a sulphide or chromate of chromium, lead, nickel orsilver. An alternative release layer is disclosed to be chromium metal.U.S. Pat. No. 4,503,112 to Konicek discloses that chromium metal releaselayers have unpredictable adhesion and that preferred release layersinclude nickel, nickel/tin alloys, nickel/iron alloys, lead and tin/leadalloys. U.S. Pat. No. 5,114,543 to Kajiwara et al. discloses a compositerelease layer having an immersion deposited chromate layer that iscoated with an electrolytically deposited copper/nickel alloy. The U.S.Pat. Nos. 3,998,601; 4,503,112 and 5,114,543 patents are incorporated byreference herein in their entireties.

[0010] U.S. Pat. No. 5,066,366 to Lin discloses forming a release layeron a copper alloy foil carrier by treating the carrier with an aqueoussolution containing chromic acid and phosphoric acid. While a generallyacceptable process, areas of unacceptable high adhesion may occur when achrome phosphate release layer is formed directly on a copper alloycarrier. U.S. Pat. No. 5,066,366 is incorporated by reference in itsentirety herein.

[0011] There remains a need for an improved release layer thatconsistently provides adequate adhesion between a carrier layer and acopper foil layer to insure that the copper foil layer remains attachedto the carrier layer during transport and processing, such as laminationto a dielectric substrate. However, the adhesion to the release layer issufficiently low that the carrier layer may be removed followinglamination without damaging the copper foil layer.

SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the invention to provide a thinmetallic foil that is releasably attached to a carrier layer. A secondobject of the invention is to provide a method for the manufacture ofthe metallic foil/carrier layer composite. A further object of theinvention is to provide a thin copper foil useful for lamination to adielectric substrate for the manufacture of printed circuit boards andflexible circuits.

[0013] It is a feature of the invention that the metal foil isreleasably attached to a carrier layer and a force of at least 0.05pound per inch is required to separate the layers thereby insuring thatthe metal foil layer is not prematurely released. It is a furtherfeature of the invention that a maximum force of 2 pounds per inch, andtypically less than 1 pound per inch, is required to separate the metalfoil layer from the carrier layer thereby facilitating removal of thecarrier layer without damage to the copper foil layer.

[0014] A further feature of the invention is that the chemical solutionsutilized for deposition of the release layer are dilute aqueoussolutions that are believed to present less of an environmental hazardthan more concentrated electrolytes previously utilized to depositrelease layers such as metallic chromium.

[0015] Among the advantages of the invention are that the metal foillayer may be a thin copper foil with a thickness of 9 microns or less.Such a thin foil facilitates the manufacture of printed circuit boardsand flexible circuits with a very fine circuit trace to circuit tracepitch. A further advantage is that the carrier layer is mechanicallyseparatable from the metal foil layer and does not require etching forremoval.

[0016] A further advantage is that the foils of the invention have lesssurface roughness than conventionally formed foils. As a result,undercutting during etching is reduced.

[0017] In accordance with the invention, there is provided a compositematerial. The composite material has a support layer and a metal foillayer. A release layer is disposed between and contacts both the supportlayer and the metal foil layer. This release layer consists essentiallyof an admixture of a metal and a non-metal.

[0018] In one embodiment of the invention, the composite material isthen laminated directly to a dielectric substrate.

[0019] There is further provided a method for the manufacture of acomposite material that includes the steps of (1) providing anelectrically conductive support layer; (2) anodically treating theelectrically conductive support layer in a first aqueous electrolytethat contains first metal ions and hydroxide ions; (3) subsequentlycathodically depositing a release layer onto the electrically conductivesupport layer in a second aqueous electrolyte that contains second metalions and hydroxide ions; and (4) electrolytically depositing a metalfoil on the release layer.

[0020] One embodiment of this method of manufacture includes theadditional steps of laminating the metal foil layer to a dielectricsubstrate and then separating the electrically conductive support layerand the release layer from the laminate. The metal foil layer, nowbonded to the dielectric layer, may then be formed into a plurality ofelectrically isolated circuit traces.

[0021] The above stated objects, features and advantages will becomemore apparent from the specification and drawings that follow.

IN THE DRAWINGS

[0022]FIG. 1 illustrates in cross-sectional representation a compositematerial in accordance with the invention.

[0023]FIG. 2 illustrates in cross-sectional representation the compositematerial of the invention laminated to a rigid dielectric as a precursorto a printed circuit board.

[0024]FIG. 3 illustrates in cross-sectional representation the compositematerial of the invention laminated to a flexible dielectric as aprecursor to a flexible circuit.

[0025]FIG. 4 is a perspective view of the printed circuit boardprecursor subsequent to removal of the carrier layer.

[0026]FIG. 5 illustrates in top planar view circuitry formed from thestructure of FIG. 4.

[0027]FIG. 6 illustrates an alternative release layer in cross-sectionalrepresentation.

DETAILED DESCRIPTION

[0028]FIG. 1 illustrates in cross sectional representation a compositematerial 10 in accordance with the invention. The composite material 10includes a support layer 12 and a metal foil layer 14. The support layer12 may be formed from any material capable of supporting the metal layer14. Preferably, the support layer 12 is formed from an electricallyconductive metal and has a thickness of at least 20 microns (1micron=1×10⁻⁶ meter). Suitable materials for the carrier layer includestainless steel, aluminum, aluminum alloys, copper and copper alloys.

[0029] Preferred for the support layer are copper alloys such as thosealloys designated by the CDA (Copper Development Association, New York,N.Y.) as copper alloy C110 (nominal composition by weight 99.95% copper(minimum) and 0.04% oxygen), copper alloy C715 (nominal composition byweight of 30% nickel and 70% copper), copper alloy C510 (nominalcomposition by weight of 94.5% copper, 5% tin and 0.2% phosphorous) andcopper alloy C102 (oxygen-free high copper having a minimum coppercontent of, by weight, 99.9%) as well as brasses, mixtures of copper andzinc containing up to 40%, by weight, of zinc.

[0030] Most preferably, the support layer 12 is a wrought material asopposed to electrolytically formed. The wrought materials tend to have ahigher strength and a higher stiffness enhancing peelability of adeposited foil. The support layer may be coated with a copper flash tocover up defects, such as incurred during rolling, that may interferewith the deposition or removal of the foil layer.

[0031] The support layer 12 may be a single material or a compositematerial with the second layer applied by any known process includingrolling, plating and sputtering. Combinations of copper and nickel andcopper and aluminum are believed useful as composite support layers.

[0032] Preferably, the thickness of the support layer 12 is from 25microns to 140 microns and more preferably from 35 microns to 70microns.

[0033] The metal foil layer 14 is any electrolytically deposited metalor metal alloy and is preferably copper. The metal foil layer typicallyhas a thickness of under 10 microns and is preferably in the range offrom about 3 to about 6 microns and nominally about 5 microns. Asdescribed below, the metal foil layer 14 may be deposited from a singleelectrolyte or from combinations of multiple electrolytes.

[0034] Disposed between and contacting both the support layer 12 and themetal foil layer 14 is a release layer 16. The release layer 16 consistsessentially of an admixture of a metal and a non-metal, with the bulkbelieved to be the non-metal. It is believed that the metal componentforms from 5% to 40%, by weight, of the release layer.

[0035] Suitable metals are those that are reversibly, electrochemically,oxidizable in a suitable electrolyte, as opposed to dissolving. The listof suitable metals includes nickel, chromium, titanium, copper,manganese, iron, cobalt, tungsten, molybdenum and tantalum.

[0036] Preferred metals are nickel, chromium and mixtures thereof.Preferred non-metals are oxides, phosphates and chromates of the metals.Preferred combinations are mixtures of chromium and chromium oxide,nickel and nickel oxide, chromium and chromium phosphate, nickel andnickel chromate, and nickel phosphate. The release layer is quite thin,on the order of 0.012 micron (120 angstroms) thick and typically fromabout 0.001 micron to about 0.03 micron thick.

[0037] Alternatively, the release layer 16 is a composite as illustratedin cross sectional representation in FIG. 6. A first portion 30 of therelease layer 16 is a metallic layer, as described above, and ispreferably selected to be nickel, chromium or a mixture thereof. Thisfirst portion 30 directly contacts the support layer 12 and is typicallydeposited by electroplating. Other methods of deposition such asimmersion plating or vapor deposition may also be utilized.

[0038] A second portion 32 of the release layer 16 is an admixture of ametal and a non-metal as described above. The second portion 32 directlycontacts the metal foil layer 14.

[0039] With reference back to FIG. 1, on a side 18 of metal foil layer14 opposite the release layer 16, a bond strength enhancing agent 20 maybe deposited. Suitable bond strength enhancing agents includeelectrolytically deposited copper dendrites having a height of betweenabout 0.5 and 2 microns and a height to diameter aspect ratio of betweenabout 3 and 10. Such dendrites may be electrolytically deposited from anaqueous solution containing copper ions and copper electrodes with thecomposite material 10 as the cathode. Pulses of DC current are appliedbetween the anode and the cathode as more fully described in U.S. Pat.No. 4,515,671 to Polan, et al., that is incorporated by reference in itsentirety herein.

[0040] Other bond strength enhancing agents include an electrolyticallydeposited mixture of chromium and zinc as disclosed in U.S. Pat. No.5,230,932 to Lin, et al., a silane based coating as disclosed in U.S.Pat. No. 5,071,520 to Lin, et al., copper oxides, mechanical abrasion ofsurfaces, alternating current etching and micro-etching.

[0041] For the manufacture of a printed circuit board, the compositematerial 10 is bonded to a dielectric substrate 22 as illustrated inFIG. 2. Metal foil layer 14 may be laminated through the addition ofheat and pressure to a rigid dielectric for the manufacture of a printedcircuit board. Typical lamination parameters are a temperature of about180° C. for 50 minutes. Optionally, a polymer adhesive may assist information of the bond. Typical rigid materials for the dielectricsubstrate include fiberglass reinforced epoxies such as FR4. Thedielectric substrate may also be an electrically conductive materialcoated with a dielectric material such as a metal cored printed circuitboard substrate or anodized aluminum.

[0042] Alternatively, as illustrated in FIG. 3, the dielectric substrate22 is a flexible polymer film such as a polyimide or polyamide. In thisinstance, the use of a polymer bond agent 24 such an acrylic or epoxypolymer is preferred. As in the preceding embodiment, metal foil layer14 is bonded to the dielectric substrate 22. Rather than laminating theflexible polymer to the metal foil layer, the flexible polymer may becast on to the metal foil layer as a liquid or gel and cured to aflexible film.

[0043] After the composite material 10 is bonded to the dielectricsubstrate 22, the carrier layer 12 and release layer 16 are removed bymechanical means. Typically, removal is by applying a force to thecarrier layer/release layer in one direction and an opposing force tothe dielectric substrate/metal foil layer in a different direction. Theforces may be either manually or mechanically applied. The forcerequired for separation, referred to as peel strength, is at least 0.05pound per inch and preferably at least 0.1 pound per inch. This minimumpeel strength is required to prevent the metal foil layer 14 fromseparating from the support layer 12 prematurely, such as duringtransport or during bonding to the dielectric substrate. The peelstrength should also be less than 2 pounds per inch and preferably lessthan 1 pound per inch to ensure that during removal the metal foil layerremains adhered to the dielectric substrate 22 and does not tear orpartially remain with composite material 10. Preferably, the peelstrength is between 0.1 pound per inch and 2.0 pounds per inch and morepreferably between about 0.2 pound per inch and 1.0 pound per inch.

[0044]FIG. 4 is perspective view of metal foil layer 14 bonded todielectric substrate 22. While FIG. 4 shows a single metal foil layerbonded to the dielectric substrate 22, additional metal foil layers maybe bonded to top surface 25 of the metal foil layer to form amulti-layer printed circuit board.

[0045] With reference to FIG. 5, the metal foil layer 14 may bechemically etched to form a plurality of conductive features such ascircuit traces 26 and die pads 28. Electrical isolation betweenconductive features is provided by dielectric substrate 22. Electricallyconductive features may be formed by any process known in the art suchas photolithography.

[0046] The following methods are useful for producing the compositematerial described above. It is recognized that variants of each methodmay be utilized and that different aspects of the various methods may bemixed together to produce a desired result. All methods generallyrequire appropriate degreasing or cleaning as a first step and rinsing,such as with deionized water, between appropriate steps.

[0047] In accordance with a first embodiment, a carrier strip formedfrom copper or a copper alloy has a thickness effective to support ametal foil layer. An exemplary nominal thickness for the carrier stripis 70 microns. The carrier strip is immersed in a dilute aqueous,alkaline sodium dichromate solution having the parameters specified inTable 1. All solutions disclosed herein are aqueous, unless otherwisespecified. When a single value is given, that value is nominal. TABLE 1Sodium hydroxide 10-50 grams per liter (g/l) (broad range) 20-35 g/l(preferred range) Chromium ions, such as from 0.1-10 g/l (broad range)sodium dichromate 0.5-5 g/l (preferred range) Operating Temperature 35°C.-50° C. pH Greater than 11 Counter Electrode Stainless steel Voltage 1volt-3 volts Current Density 0.5-10 amps per square foot Anodic step(ASF) (broad range) 1-5 ASF (preferred range) Current Density 0.5-40amps per square foot Cathodic step (ASF) (broad range) 1-20 ASF(preferred range) Time (anodic step) 1-60 seconds (broad range) 5-20seconds (preferred) Time (cathodic step) 1-60 seconds (broad range) 5-20seconds (preferred)

[0048] The carrier strip is immersed into an electrolytic cellcontaining the electrolyte and a voltage is impressed across the cellwith the carrier strip as the anode. The anodic treatment generates auniform microroughness on the surface of the carrier strip and induces asubsequent uniform metal foil layer copper deposit. On completion of theanodic treatment, the carrier strip is maintained in the sameelectrolyte and the polarity of the electrolytic cell is reversed. Thecarrier strip is made the cathode to deposit a thin, on the order of10-300 angstrom, layer that is believed to be an admixture of chromiumand chromium oxides on the carrier strip. This admixture forms therelease layer that facilitates separation of the carrier stripsubsequent to lamination or other processing.

[0049] The release layer is formed to a maximum thickness of about 300angstroms. When the release layer thickness exceeds this maximum, theminimum peel strength requirements are not consistently achieved. Sincethe thickness of the release layer may be less than the microscopicsurface roughness of the copper foil, the precursor anodic treatment isused to achieve a more uniform surface finish.

[0050] Subsequent to rinsing, a seed layer of copper with a nominalthickness of between 0.2 and 0.5 micron of copper is deposited on therelease layer utilizing the parameters specified in Table 2. TABLE 2Copper ions, such as from 5-35 g/l (broad range) copper sulfate and/or15-25 g/l (preferred copper pyrophosphate range) Optional inclusions ofAmount as required leveling agents, complexing agents and surfactantsOperating Temperature 35° C.-70° C. pH 6-10 Anode Material StainlessSteel or copper Voltage 3-7 volts Current Density 10-50 ASF Time 40-100seconds

[0051] The seed layer forms a nucleating agent for the subsequent highspeed deposition of a copper foil layer. While the seed layer ispreferably formed from copper, it may be any electrically conductivemetal that is etchable in the same chemical solutions as copper. Suchother metals for the seed layer include copper alloys, chromium,molybdenum, tungsten, nickel, cobalt, etc. The seed layer protects therelease layer from chemical attack in an electrolyte utilized to depositthe bulk of the metal foil layer thickness. Typically, to maximizemanufacturing speed, an acid copper electrolyte as specified in Table 3is utilized. TABLE 3 Copper ions, such as from 20-80 g/l (broad) coppersulfate 50-70 g/l (preferred) Sulfuric acid 30-200 g/l (broad) 40-100g/l (preferred) Operating Temperature 25° C.-60° C. pH Less than 1.5Anode Material Lead or copper Voltage 5-10 volts Current Density 30-1000ASF (broad) 40-500 ASF (preferred) Time 1-8 minutes (broad) 2-5 minutes(preferred)

[0052] To enhance adhesion, a dendritic treatment may be used to roughenthe outside surface of the metal foil layer. One suitable dendritictreatment utilizes the parameters specified in Table 4. Alternatively,an anti-tarnish layer such as a mixture of chromium and zinc may bedeposited to increase adhesion without increasing surface roughness.TABLE 4 Copper ions, such as from 15-70 g/l (broad) copper sulfate 18-25g/l (preferred) Sulfuric acid 10-200 g/l (broad) 35-100 g/l (preferred)Operating Temperature 25° C.-55° C. pH Less than 1.5 Anode Material Leador copper Voltage 5-10 volts Current Density 50-1000 ASF (broad) 100-500ASF (preferred) Time 4-30 seconds (broad) 4-10 seconds (preferred)

[0053] In a second embodiment, a carrier strip as described above isimmersed in the solution of Table 1 for a time of from two to sixtyseconds without utilizing electric current. A nominal 5 micron copperfoil layer and dendritic treatment is then applied as above.

[0054] In accordance with a third embodiment of the invention, a coppercarrier strip, as described above, is electrolytically coated with athin, on the order of between 0.05 micron and 2 microns, layer of nickelutilizing the parameters described in Table 5. TABLE 5 Nickel sulfamate150-600 g/l (broad) 400-500 g/l (preferred) Nickel chloride 0-15 g/lBoric acid 25-50 g/l (broad) 35-45 g/l (preferred) Operating Temperature45° C.-60° C. pH 2-5 Anode Material Nickel or Stainless Steel Voltage0.5-5 volts Current Density 20-60 ASF Time 20-60 seconds

[0055] A chromium phosphate release layer is then applied over the thinlayer of nickel by immersion in a dilute chromic acid/phosphoric acidsolution having the parameters disclosed in Table 6. TABLE 6 Chromicacid 0.1-20 g/l (broad) 0.2-10 g/l (preferred) Phosphoric acid 0.1-80g/l (broad) 0.5-40 g/l (preferred) Operating Temperature 20° C.-60° C.pH 0.1-3 Time 5-120 seconds (broad) 10-40 seconds (preferred)

[0056] A nominal 5 micron copper foil metal layer is then deposited asabove followed by a dendritic treatment as above.

[0057] In accordance with a fourth embodiment of the invention, a thin,on the order of between 0.05 micron and 2 microns, layer of nickel isdeposited on a copper alloy carrier strip as above. A release layer isdeposited from an aqueous solution containing sodium dioxide asdisclosed in Table 7. TABLE 7 Sodium hydroxide 10-80 g/l (broad) 20-50g/l (preferred) Operating Temperature 35° C.-60° C. pH Greater than 11Counter Electrode Stainless steel or nickel Voltage 0.5-5 volts CurrentDensity (anodic 10-50 ASF (broad) step) 25-35 ASF (preferred) CurrentDensity (cathodic 5-40 ASF (broad) step) 10-25 ASF (preferred) Time(anodic step) 2-60 seconds 5-30 seconds Time (cathodic step) 2-60seconds 5-30 seconds

[0058] The nickel coated carrier strip is first made anodic and thencathodic to form reduced nickel oxides. Approximately 5 microns ofcopper is then applied as the metal foil layer followed by a dendritictreatment as described above.

[0059] In each of embodiments 1-4, an alkaline copper plating bath waspreferably used to deposit a seed layer having a thickness of from about0.2 to about 0.5 micron of copper prior to depositing up to 5 microns ofcopper plating in an acidic bath. The initial use of an alkaline copperbath avoids potential attack to the chromium oxide, nickel oxide ornickel phosphate release layer as could happen in the acidic copper baththus improving the reliability/integrity of the release interface.Embodiments five and six describe methods for forming a compositematerial having similar reliability and integrity without the need foran alkaline copper bath.

[0060] In embodiment five, a smooth nickel deposit is formed on thecopper alloy carrier strip utilizing a suitable nickel plating bath,such as the nickel sulfamate electrolyte of Table 5. The nickel platedcarrier strip is then immersed in an aqueous electrolyte containingsodium hydroxide utilizing the parameters recited in Table 6. Thecarrier strip is first made anodic and then cathodic. A copper metalfoil layer is then deposited using a copper sulphate bath (Table 3)followed by dendritic treatment (Table 4).

[0061] In a sixth embodiment, a thin layer of nickel, having a thicknesson the order of between 0.05 micron and 2 microns, is applied to thecarrier strip (Table 5) as described above followed by treatment in anaqueous solution containing sodium hydroxide with the carrier stripfirst forming the anode and then the cathode as in Table 5. Next, thenickel is treated cathodically in an acid copper sulfate bath at lowcurrent density and the parameters illustrated in Table 8. TABLE 8Copper ions, such as from 40-80 g/l (broad) copper sulfate 60-70 g/l(preferred) Sulfuric acid 50-100 g/l (broad) 60-75 g/l (preferred)Operating Temperature 35° C.-60° C. pH Less than 1 Cathode Material Leador copper Voltage 5-8 volts Current Density 0.03-2 ASF (broad) 0.05-0.5ASF (preferred) Time 30-120 seconds (broad) 45-90 seconds (preferred)

[0062] Copper deposition as in Table 3 is then utilized to increase thethickness up to a nominal 5 microns. Dendritic treatment as in Table 4completes the process.

[0063] Composite materials formed from any one of the above processesmay then be used to manufacture either printed circuit boards or flexcircuits as described above. The advantages of the invention will becomemore apparent from the examples that follow.

EXAMPLES Example 1

[0064] A 2 oz. wrought copper foil was used as a carrier strip. Thestrip was electrocleaned in an alkaline commercial cleaner using 20 ASFcurrent density for 40 sec. The foil was rinsed and then the releaselayer treatment was conducted in 20-35 g/l NaOH+0.5-5 g/l chromium ionsas sodium dichromate solution using an anodic current of 1-5 ASFfollowed by a cathodic current of 1-20 ASF for 5-20 sec. The anodictreatment appeared to generate a uniform micro-roughness on the surfaceof the foil and induce a uniform copper deposit. The cathodic treatmentappeared to deposit a transparent layer of chromium and chromium oxides,which is believed to be responsible for the release of the carrier stripafter lamination.

[0065] A seed layer of 0.2-0.5 micron copper was electroplated in analkaline copper plating solution. A 5 micron copper deposit was thenelectroplated, using 60-70 g/l copper ions as copper sulfate and 60-75g/l sulfuric acid at 40-100 ASF for 5.4-2.1 minutes, followed by adendritic copper or copper/nickel treatment. After lamination to an FR-4epoxy substrate, the 2 oz carrier was easily peeled with a measured bondstrength of 0.1-1.0 lb/in.

Example 2

[0066] A 2 oz. wrought copper foil was used as a carrier strip. Thestrip was electrocleaned in an alkaline commercial cleaner using 20 ASFcurrent density for 40 sec. The foil was rinsed and then the releaselayer treatment applied by electroplating in a solution of 20-35 g/lNaOH+0.5-5 g/l chromium ions as sodium dichromate. This treatmentappeared to form a transparent layer of chromium and chromium oxides.

[0067] A seed layer of 0.2-0.5 micron copper was electroplated in analkaline copper plating solution. A 5 micron copper deposit was thenelectroplated using 60-70 g/l copper ions as copper sulfate and 60-75g/l sulfuric acid at 40-100 ASF for 5.4-2.1 minutes, followed by adendritic copper or copper/nickel treatment. After lamination to an FR-4epoxy substrate, the 2 oz. carrier was easily peeled with a measuredbond strength of 0.1-1.0 lb/in.

Example 3

[0068] After cleaning the copper carrier strip, a nickel layer was firstelectroplated with 0.15 micron nickel in a nickel sulfamate bath at 30ASF for 20 sec. The foil was then immersed in a solution containing0.2-10.0 g/l chromic acid and 0.5-40 g/l phosphoric acid for 10-40 secat ambient temperature. The alkaline copper seed layer and acidic copperplating were conducted as described in Example 1. A peelable foilresulted after lamination with 0.2-2.0 lb/in release force.

Example 4

[0069] As in Example 2, a nickel layer was first electroplated. Thenickel surface was then anodically treated in a 20-50 g/l NaOH solutionat 0.5-10 ASF for 5-30 sec to generate a nickel oxide release layer.This nickel oxide layer was then cathodically reduced in a 20-50 g/lNaOH solution at 0.5-50 ASF for 5-30 sec. This cathodic treatmentappeared to produce reduced oxides and enlarge the operating window.Without the cathodic treatment, if the anodic current is too low, anon-peelable foil would be produced. If the anodic current is too high,the plated 5 micron foil often delaminates or forms blister even beforelamination and renders the product useless.

[0070] After the nickel and nickel oxide treatment, the alkaline copperseed layer and 5 micron acidic copper are deposited. A release force of0.35-1.0 lb/in was obtained.

Example 5

[0071] Use of a copper seed layer may be problematic from the standpointof foil production for other reasons not the least of these is the factthat the process uses non-consumable (stainless steel) anodes. Henceduring operation of a production line, the copper content of theelectrolyte must be held constant by the addition of soluble copperions. Such occurs by the additions of appropriate replenishment saltssupplied by the manufacturer of the plating bath. Thus while the bathcopper content can be maintained, the concentration of other chemicalspecies (pyrophosphate, phosphate, sulfate, etc.) must increase. In thisexample, the inventors have identified an approach that is accomplishedwithout need for a seed layer from an alkaline copper bath.

[0072] The formation of a smooth nickel deposit onto a carrier strip hasbeen shown to be very easily accomplished by deposition out of a nickelsulfamate bath using a current density of 30 to 50 ASF with times of 20to 30 seconds.

[0073] Treatment of the nickel plate in a solution of 30 g/l sodiumhydroxide was then conducted with an anodic treatment of 20 to 40 ASFfor 20 to 40 seconds with subsequent cathodic treatment in the samesolution at 25% to 50% of the anodic current density and for half thetime. No seed layer was used, rather the nickel coated support layer wascathodically treated in acid-copper sulfate bath at low current density,60 seconds at 0.03 to 2 ASF, followed by plating of copper from the acidcopper sulfate bath at 65 ASF for 3.5 minutes to achieve the desired 5micron thickness. The foils retained their peelability followinglamination.

[0074] For comparison, it was demonstrated that the above low currenttreatment resulted in peelable foils free of defects while foils madeusing identical conditions, but without the low current treatment, werefull of defects and not peelable following lamination.

[0075] It is apparent that there has been provided in accordance withthe present invention a composite material including a releasable metalfoil layer and methods for the manufacture of such a composite materialthat fully satisfies the objects, means and advantages as set forthherein above. While the invention has been described in combination withembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art in light ofthe foregoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications and variations as fall within thespirit and broad scope of the appended claims.

We claim:
 1. A composite material, comprising: a support layer; a metalfoil layer; and a release layer disposed between and contacting bothsaid support layer and said foil layer, said release layer consistingessentially of an admixture of a metal and a non-metal.
 2. The compositematerial of claim 1 wherein said release layer is an admixture of ametal selected from the group consisting of chromium, nickel, titanium,copper, manganese, iron, cobalt, tungsten, molybdenum, tantalum andmixtures thereof and said non-metal is selected from the groupconsisting of oxides, phosphates and chromates of said metal.
 3. Thecomposite material of claim 2 wherein said release layer is an admixtureof a metal selected from the group consisting of chromium, nickel andmixtures thereof and said non-metal is selected from the groupconsisting of oxides, phosphates and chromates of said metal.
 4. Thecomposite material of claim 3 wherein said release layer is an admixtureselected from the group consisting of chromium and chromium oxide,nickel and nickel oxide, chromium and chromium phosphate, nickel andnickel phosphate, and nickel and nickel chromate.
 5. The compositematerial of claim 4 wherein said release layer has a thickness ofbetween 0.001 micron and 0.03 micron.
 6. The composite material of claim3 wherein said release layer is an admixture of chromium and chromiumoxide.
 7. The composite material of claim 6 wherein said admixtureincludes from 5% to 40%, by weight, of chromium.
 8. The compositematerial of claim 4 wherein said support layer has a first portionselected from the group consisting of stainless steel, aluminum,aluminum alloys, copper and copper alloys.
 9. The composite material ofclaim 8 wherein said support layer is a composite with a copper orcopper alloy first support layer portion and a nickel, aluminum, nickelalloy or aluminum alloy second support layer portion.
 10. The compositematerial of claim 8 wherein said support layer first portion is copperor a copper alloy.
 11. The composite material of claim 8 wherein saidmetal foil layer is copper with a thickness of less than 10 microns. 12.The composite material of claim 11 wherein said metal foil layer iscopper with a thickness of between 3 microns and 6 microns.
 13. Thecomposite material of claim 11 wherein said metal foil layer is coatedwith a bond strength enhancing agent.
 14. The composite material ofclaim 13 further including a dielectric substrate bonded to said metalfoil layer with said bond strength enhancing agent disposed therebetween.
 15. A composite material, comprising: a support layer; a metalfoil layer; and a release layer disposed between and contacting bothsaid support layer and said foil layer, said release layer having ametallic first portion adjacent said support layer and a second portion,adjacent said metal foil layer that consists essentially of an admixtureof a metal and a non-metal.
 16. The composite material of claim 15wherein said release layer first portion is selected from the groupconsisting of chromium, nickel, titanium, copper, manganese, iron,cobalt, tungsten, molybdenum, tantalum and mixtures thereof.
 17. Thecomposite material of claim 16 wherein said release layer first portionis selected from the group consisting of nickel, chromium and mixturesthereof.
 18. The composite material of claim 17 wherein said releaselayer second portion is an admixture of a metal selected from the groupconsisting of chromium, nickel and mixtures thereof and said non-metalis selected from the group consisting of oxides, phosphates andchromates of said metal.
 19. The composite material of claim 18 whereinsaid release layer second portion is an admixture selected from thegroup consisting of chromium and chromium oxide, nickel and nickeloxide, chromium and chromium phosphate, nickel and nickel phosphate, andnickel and nickel chromate.
 20. The composite material of claim 19wherein said release layer has a total thickness of between 0.001 micronand 0.03 micron.
 21. The composite material of claim 19 wherein saidrelease layer second portion is an admixture of chromium and chromiumoxide.
 22. The composite material of claim 19 wherein said release layersecond portion is an admixture of chromium and chromium phosphate. 23.The composite material of claim 19 wherein said support layer has afirst portion selected from the group consisting of stainless steel,aluminum, aluminum alloys, copper and copper alloys.
 24. The compositematerial of claim 23 wherein said support layer is a composite with acopper or copper alloy first support layer portion and a nickel,aluminum, nickel alloy or aluminum alloy second support layer portion.25. The composite material of claim 23 wherein said support layer firstportion is copper or a copper alloy.
 26. The composite material of claim23 wherein said metal foil layer is copper with a thickness of less than10 microns.
 27. The composite material of claim 26 wherein said metalfoil layer is copper with a thickness of between 3 microns and 6microns.
 28. The composite material of claim 26 wherein said metal foillayer is coated with a bond strength enhancing agent.
 29. The compositematerial of claim 28 further including a dielectric substrate bonded tosaid metal foil layer with said bond strength enhancing agent disposedthere between.
 30. A method for the manufacture of a composite materialcomprising the steps of: providing an electrically conductive supportlayer; anodically treating said electrically conductive support layer ina first aqueous electrolyte containing first metal ions and hydroxideions; subsequent to said anodically treating step, cathodicallydepositing a release layer onto said electrically conductive supportlayer in a second aqueous electrolyte containing second metal ions andhydroxide ions; and electrolytically depositing a metal foil layer onsaid release layer.
 31. The method of claim 30 wherein said firstaqueous electrolyte is selected to contain 'sodium hydroxide andchromium ions.
 32. The method of claim 31 wherein said cathodicallydepositing step is effective to deposit an admixture of chromium andchromium oxide having a thickness of up to 300 angstroms.
 33. The methodof claim 32 wherein said electrolytically depositing a metal foil layerstep includes first depositing a copper seed layer from an alkalinecopper electrolyte and then depositing a bulk copper layer from anacidic copper electrolyte.
 34. The method of claim 33 wherein said metalfoil layer is formed to a total thickness of less than 10 microns withsaid copper seed layer formed to a thickness of between 0.2 micron and0.5 micron.
 35. The method of claim 34 including the further steps oflaminating said metal foil layer to a dielectric substrate and thenseparating said electrically conductive support layer and said releaseagent from a laminate comprising said dielectric substrate and metalfoil layer.
 36. The method of claim 35 including the further step offorming said metal foil layer into a plurality of electrically isolatedcircuit traces.
 37. A method for the manufacture of a composite materialcomprising the steps of: providing an electrically conductive supportlayer; forming a release layer on said electrically conductive supportlayer, said release layer having a first portion adjacent saidelectrically conductive support layer that is a metal selected from thegroup consisting of nickel, chromium and mixtures thereof and a secondportion that is an admixture of a metal and a non-metal; andelectrolytically depositing a metal foil layer on said release layer.38. The method of claim 37 wherein said first portion iselectrolytically deposited and said second portion is an immersioncoating admixture of chromium and chromium phosphate.
 39. The method ofclaim 38 wherein said electrolytically depositing a metal foil layerstep includes first depositing a copper seed layer from an alkalinecopper electrolyte and then depositing a bulk copper layer from anacidic copper electrolyte.
 40. The method of claim 39 wherein said metalfoil layer is formed to a total thickness of less than 10 microns withsaid copper seed layer formed to a thickness of between 0.2 micron and0.5 micron.
 41. The method of claim 37 wherein said first portion iselectrolytically deposited and said second portion is anelectrolytically formed admixture of nickel and nickel oxide.
 42. Themethod of claim 41 wherein said electrolytically depositing a metal foillayer step includes first depositing a copper seed layer from analkaline copper electrolyte and then depositing a bulk copper layer froman acidic copper electrolyte.
 43. The method of claim 42 wherein saidmetal foil layer is formed to a total thickness of less than 10 micronswith said copper seed layer formed to a thickness of between 0.2 micronand 0.5 micron.
 44. The method of claim 41 wherein said electrolyticallydepositing a metal foil layer step includes first depositing a thincopper layer from an acidic copper electrolyte at a first currentdensity of less than two ASF and then depositing a bulk copper layerfrom an acidic copper electrolyte at a second current density of atleast 30 ASF.
 45. The method of claim 44 wherein said first currentdensity is from 0.03 to 2 ASF and said second current density is from 30to 150 ASF.